1. Field of the Invention
The present invention concerns an MR-inductive composite type thin-film magnetic head which is integrally equipped with an inductive head used for recording and a magneto-resistive head (MR head) used for playback.
2. Background Information
Devices such as computers and word processors, etc., have become widespread in Japanese industry, and magnetic memory devices contained in such devices have continued to increase in capacity. As the capacity of magnetic memory devices has increased, there has been a demand for improved recording-playback performance in thin-film magnetic heads.
Under such conditions, composite type thin-film magnetic heads which are integrally equipped with an inductive head used for recording and a magneto-resistive head (MR head) have been proposed instead of conventional inductive heads.
The layer construction of a composite type thin-film magnetic head is as shown in FIGS. 11 and 12. In such a head, an inductive head used for recording and a magneto-resistive head used for playback are integrally laminated.
Specifically, in a composite type thin-film magnetic head, an inductive head used for recording is formed by the upper-side portion in the figures (i. e., the portion indicated by bracket A in FIG. 12). Furthermore, a magneto-resistive element 5 is contained in the layers beneath this inductive head, so that a magneto-resistive head B is formed by this portion.
The respective layers will be concretely described below.
In a composite type thin-film magnetic head, a substrate 6 consisting of an Al.sub.2 O.sub.3 -TiC ceramic, etc., is used as a base, and an insulating film 7 consisting of Al.sub.2 O.sub.3 is formed on this substrate 6. Furthermore, a first magnetic film layer 8 is laminated on the surface of the insulating film 7. Moreover, this first magnetic film layer 8 is referred to as the "lower shielding magnetic film." In addition, the magneto-resistive element 5 is embedded in this first magnetic film layer 8.
The magneto-resistive element 5 is a member which has a type of electro-magnetic effect such that when the material is magnetized, the electrical resistance of the material changes. Materials which have such a magneto-resistive effect include NiFeE, NiFeCo, NiCo, FeMn, Fe.sub.3 O.sub.4, CoPt/Cr and Fe/Cr, etc. The material used for the magneto-resistive element 5 is appropriately selected from these materials.
A second magnetic film layer 10 is formed on top of the magneto-resistive element 5. This second magnetic film layer 10 is laminated over substantially the entire surface area of the substrate 6. Furthermore, this second magnetic film layer 10 is also referred to as the "upper shielding magnetic film."
Moreover, a magnetic gap film layer 11 is formed on the surface of the second magnetic film layer 10, and a third magnetic film layer 12 is laminated so that this magnetic gap film layer 11 is sandwiched between the third magnetic film layer 12 and the second magnetic film layer 10. Furthermore, this third magnetic film layer 12 is also referred to as the "recording inductive magnetic film layer" 12.
A protective layer 18 is disposed on top of the third magnetic film layer 12.
The plan-view shapes of the magnetic gap film layer 11 and third magnetic film layer 12 are as shown in FIG. 11. These layers are formed so that the tip end portions (where the magnetic gap is formed) are narrow, while the inside portions of the layers have a somewhat larger area. Furthermore, in the inside portions of the composite type thin-film magnetic head, as is shown in FIGS. 11 and 12, the third magnetic film layer 12 is in a positional relationship which is such that the third magnetic film layer 12 is separated from the second magnetic film layer 10 and magnetic gap layer 11, and an insulating film 14, conductive coil film 15 and insulating film 16 are interposed between the second magnetic film layer 10 and third magnetic film layer 12. Furthermore, the second magnetic film layer 10 and third magnetic film layer 12 are joined in the area of the rear gap 20 located toward the rear, and the conductive coil film 15 is disposed in the form of a coil centered on the rear gap 20 as shown in FIG. 11.
Meanwhile, the front end portions of the second magnetic film layer 10 and third magnetic film layer 12 face each other across the magnetic gap film layer 11, thus forming a magnetic gap in this area.
In this composite type thin-film magnetic head, during recording, a signal current is applied to the conductive coil film 15, so that magnetic flux is generated in the magnetic gap at the tip end where the third magnetic film layer 12 and second magnetic film layer 10 face each other. Accordingly, the signal is written on the magnetic medium 22.
During playback, magnetic flux from the magnetic medium 22 passes between the first magnetic film layer 8 and the second magnetic film layer 10 with the same timing that the magnetization transition regions on the magnetic medium 22 pass through. Accordingly, the resistance of the magneto-resistive element 5 which is located between the first magnetic film layer 8 and second magnetic film layer 10 varies so that a playback signal is output.
In magnetic recording, a magnetic medium material such as a magnetic disk, etc., is magnetized, and the residual magnetization remaining in this magnetic disk, etc., is utilized for recording. Accordingly, it is desirable that a sufficient magnetic flux be produced across the entire track width in the magnetized portions.
Specifically, it is desirable that the magnetic medium be uniformly magnetized in the direction of track width as shown in FIG. 1 3A, and that an output waveform be readable from the entire writing width as shown in FIG. 13B.
In actuality, however, the intensity of the magnetic field output by the recording head is weak at both edges of the track width, and there are also effects of leakage magnetic flux. Accordingly, the residual magnetization at the edges of the track width is weak as shown in FIG. 14A. As a result, as is shown in FIG. 14B, it is currently impossible to read the output waveform at both edges of the track width. Specifically, portions known as the "erase width," in which an output waveform is not produced, are formed at both edges of the writing width.
In other words, the erase width portions are regions in which no output waveform is produced, and are dead zones with respect to magnetic recording. Accordingly, in cases where the erase width is large, there is a corresponding drop in the ability to achieve a high recording density (high TIP). This is a major factor hindering the achievement of a high track density.
In addition, in the case of conventional composite type thin-film magnetic heads, the shape of the magnetization transition regions is oval, and the problem of a high noise level arises. Specifically, in the case of conventional composite type thin-film magnetic heads, the shape of the magnetization transition regions is not rectangular, but is close to "U" shaped. The cause of this will be explained below.
FIG. 15 is an explanatory diagram which shows the orientation of the magnetic flux in the vicinity of the magnetic gap of a conventional thin-film magnetic head in model form. FIGS. 16A-C are explanatory diagrams which show the shape of the magnetic field above and below the gap of a conventional thin-film magnetic head, and the magnetization transition regions, in model form. FIG. 16A shows the shape of the magnetic field above and below the gap of the thin-film magnetic head. The area surrounded by a frame is the range in which the coercive force Hc of the magnetic medium 22 is exceeded. Furthermore, FIG. 16B shows the shape of the magnetic field of the magnetic medium 22 in the initial stage of magnetization, and FIG. 16C shows a magnetization transition region on the magnetic medium 22.
In the magnetic gap area, magnetic flux emerges in a direction substantially perpendicular to the magnetic medium 22 at the end surfaces of the magnetic film layers (ABS surface side of the slider), as is indicated by the arrows in the central portion of FIG. 15. However, as is shown by the arrows at both ends in FIG. 15, magnetic flux emerges in a direction parallel to the gap from the areas in the vicinity of both end portions of the third magnetic film layer. As a result, the shape of the magnetic field in the vicinity of gap is a shape such as that shown in FIG. 16A, so that the magnetic field in the vicinity of the third magnetic film layer has a "U" shape in which both ends are slightly raised.
In the initial stage of magnetization, the magnetic medium 22 is magnetized as shown in FIG. 16B. Ultimately, however, since the magnetization transition regions which remain on the surface of the magnetic medium 22 are determined by the shape of the magnetic field in the upper portion of the gap as shown in FIG. 16C, the magnetization transition regions 40 assume a shape in which both ends are raised as shown in the figures. Furthermore, this edge shape increases the playback pulse width so that the resolution is caused to deteriorate. Moreover, since this edge shape is a source of noise, there are also problems in terms of a poor signal-to-noise ratio, etc. Such problems are an obstacle to any increase in the recording density.
Accordingly, noting the above-mentioned problems, the object of the present invention is to develop a composite type thin-film magnetic head which makes it possible to reduce the erase width and improve the shape of the magnetization transition regions, so that a high recording density can be realized.